Huge numbers of brain cells may navigate small worlds

            Modeling the brain as a network is just one of the ways in which people have tried to understand the brain.  A “small world” idea was first introduced around forty years ago by Stanley Milgram, who created a study in which participants attempt to send a folder a target individual through other friends and acquaintances.  Of the successful fourth, there was an average of six intermediate nodes (people).  In the late 1990’s, Milgram’s study was followed up by Steven Strogatz (Cornell University) and Duncan Watts (NYU) through simulations involving electric-power grids, actor’s relationships, and ultimately to the 282 brain cells of nematodes (worms).  Neuroscientists have adopted these methods to model the human brain in the small-world setups that are so common elsewhere in the world.  

            In a study by Danielle Bassett, volunteers had sensors at 275 points across their scalp to measure the magnetic field produced by the electrical discharges of neurons.  Six types of brain waves showed up at a different frequency.  From this data the neural network was reconstructed and a “small world” arrangement was seen.  Like so many of the social structures encountered already in this class, the brain obviously turns out to be just like them; there are large clusters of neurons that have a few connections to other clusters.  These interactions between networks act as a unique path for each electrical frequency, and the two highest frequencies during a finger tapping test became synchronized at a certain point during their path.  Supporting the claims made by Mark S. Granovetter in The Strength of Weak Ties, the not-as-strong connections to other clusters help in allowing for the fast transfer of signals between clusters of neurons all the way to the other side of the brain.

            An interesting point brought up in this article is that every brain wave looked similar but just operated on its unique scale.  The fractal-like brain network, when at a high enough frequency, “operates on the edge of chaos.”  According to Walter J. Freeman (University of California, Berkeley), this chaotic behavior is what the brain thrives on.  The article doesn’t go into much more detail about this fractal behavior, but it will be interesting to see more results and conclusions of studies on this.